Dynamoelectric machines



Ju 8, 1968 R. L. JAESCHKE ,2

DYNAMOELECTRIC MACHINES Filed Dec. 28, 1965 6 Sheets-Sheet 1 June- 18,1968 R. 1.. JAESCHKE 3, 8

DYNAMOELECTRIC MACHINES Filed Dec. 28, 1965 6 Sheets-Sheet 2 FIGS.

June 18, 1968: R. JAESCHKE 3,389,278

DYNAMOELECTRIC MACHINES Filed Dec. 28, 1965 e Sheets-Sheet. s

FIG.6.

June 18, 1968 R. JAESCHKE 3,389,278

DYNAMOELECTRIC MACHINES I Filed Dec. 28, 1965 e Sheets-Sheet 4 FIGS.

I FIG. I0.

800 Y FREQUENCY CYCLES PER SECOND June 18, REL. JAESCHKE 3,389,278-

' DYNAMOELECTRIC MACHINES Filed Dec. 28, 1965. e Sheets-Shet s Q) h s lI Q X o a h United States Patent 3,389,278 DYNAMOELECTRIC MACHINES RalphL. .laeschke, Kenosha, Wis., assignor to Eaton Yale & Towne Inc., acorporation of Ohio Continuation-impart of application Ser. No. 456,094,May 17, 1965. This application Dec. 28, 1965, Ser. No. 528,675

28 Claims. (Cl. 310-105) ABSTRACT OF THE DISCLOSURE Assemblies aredisclosed for suppressing sound generated by the relatively rotarymembers of air or gas-cooled dynamoelectric machines, such as motors anddynamometers. The assembly is constituted by a housing with one or moreair inlet passages connected to one or more air inlet openings of themachine. The housing also includes one or more air outlet passagesconnected to one or more air outlet openings of the machine. Each inletand outlet passage is provided with a cross wall positioned transverselyto the direction of air flow and has an aperture smaller than therespective air inlet and outlet openings. These cross walls arepositioned in the passages in a direction away from the openings and ata distance substantially equal to a wavelength function of thecharacteristic frequency of the sound in the air circulating through therespective passages. Sound suppressors having more than one aperturedcross wall are described for effecting substantial cancellation of soundof more than one characteristic frequency.

This application is a continuation-in-part of my copending US. patentapplication Ser. No. 456,094, filed May 17, 1965, and now abandoned, forElectromagnetic Induction Apparatus Including Sound Suppressor Means.

This invention relates to dynarnoelectric machines, and moreparticularly to such machines comprising rotary electromagneticinduction apparatus and sound suppression means therefor.

Among the several objects of the invention may be noted the provision ofsound suppressor means in connection with electromagnetic inductionapparatus, the latter being cooled by air or other gas, said suppressormeans being particularly effective when several energy peaks of soundresulting in noise are to be suppressed; the provision of eflicientlycooled electromagnetic induction apparatus having such sound suppressormeans compactly forming a part thereof; the provision of apparatus ofthe class described which is so constructed that its parts may beflexibly arranged for various conditions at the point of use; and theprovision of low-cost sound suppressor means per se. Other objects andfeatures will be in part apparent and in part pointed out hereinafter.

The invention accordingly comprises theelements and combinations ofelements, features of construction, and arrangements of parts which willbe exemplified in the constructions hereinafter described, and the scopeof which will be indicated in the following claims.

In the accompanying drawings, in which several of various possibleembodiments of the invention are illustrated.

FIG. 1 is an end elevation of an air-cooled eddy-current couplingillustrating the invention;

FIG. 2 is a left side view of FIG. 1;

FIG. 3 is an enlarged partial section viewed on line 3--3 of FIG. 1,showing air-cooled electromagnetic coupling means;

FIG. 4 is a vertical section taken on line 4-4 of FIG. 3, showingair-circulating means;

Patented June 18, 1968 "ice FIGS. 5 and 6 are vertical sections taken onlines 5-5 and 66, respectively, of FIG. 2, showing a preferred shallowform of sound suppressor means;

FIG. 6A is an enlarged fragmentary view of the lower part of FIG. 6,illustrating the use, if desired, of acoustical lining material;

FIGS. 7 and 8 are views similar to FIGS. 5 and 6, respectively, showingan alternative long form of sound suppressor means;

FIG. 9 is a small-scale, diagrammatic end view like FIG. 1, illustratingby dotted lines various modes of attachment to induction apparatus ofthe sound suppressor means;

FIG. 10 is a substantially logarithmic chart showing typicalimprovements brought about by means of the invention;

FIG. 11 is a side elevation of another embodiment of a sound suppressorassembly of this invention;

FIGS. 12 and 13 are vertical sections taken on lines 12-12 and 1313 ofFIG. 11; and

FIG. 14 is a vertical section on lines 1414 of'FIG. 12 showing portionsof the assembly in phantom.

Corresponding reference characters illustrate corresponding partsthroughout the several views of the drawings.

The term electromagnetic induction apparatus as used herein is intendedto include electromagnetic induction couplings such as illustrated,motors, dynamometers, etc., which have two relatively rotary memberswhich generate heat during relative rotation, and which employair orother suitable gas as a coolant. The terms air and gas are to be takenherein as synonymous.

In view of water shortages and cost, it has become the practice toemploy air or gas rather than water or other costly liquid coolant forthe cooling of induction apparatus of the types above-mentioned,particularly in those cases wherein the apparatus is of high capacityand in which substantial amounts of heat are generated and are requiredto be dissipated and carried off. The airdriving fin arrangements forhigh-capacity performance produce a high sound level which often haspeaks at one or more different frequencies. The result is a high levelof what is generally referred to as noise, which is of a disagreeablenature, so much so that in many instances it becomes intolerable inlocations where the machines are installed. This has resulted in theproblem of incorporating a substantially effective, compact soundsuppressor which may be constructed economically and which will meetdemands at various locations in the field. The present inventioneffectively solves these and connected problems.

Referring now more particularly to FIGS. 14, numeral 1 indicates atypical eddy-current electromagnetic induction coupling. Such a couplingincludes a substantially constant-speed driving motor '3 having a driveshaft 5 (FIGS. 2 and 3). The flange 7 of the motor is bolted to anupright rectangular end wall 9, supported near one end of a base 11. Theshaft 5 is supported on the usual bearings located in the motor casing.Carried near the other end of the base 11 is a second rectangular endwall 13 which supports an end bell 15. The end bell is a bearing 17 fora driven shaft 19. Wall 9 is braced by stiffening flange means 10extending from base 11, and wall 13 by stiffening flange means 14extending from the base.

The driven shaft 19 carries a polar field member 21 havinginterdigitated pole-forming teeth 23 excited by a stationary field coil25. Coil 25 is carried on brackets 27 extending from the end ibell 15.The end wall 13 has an opening 29 for accommodating insertion of thebrackets 27 and other parts. The end bell 15 also carries stator 31 of atachometer control generator, the rotor 32 of which is carried by shaft19. The stator 31 is wired in the usual way to control the fieldstrength of the electromagnetic coil 25. Thus the polar field strengthof the polar field member 21. controls the speed of shaft 19. The speedof shaft is substantially constant. An air-temperature sensor 34 is alsocarried on the end bell and extends interiorly through the opening 29and a peripheral air bafile 30.

Surrounding the field poles 23 is a ferromagnetic eddycurrent inductordrum 33. This is welded to and supported by a rotary spider 35 (FIG. 4),having a hub 37 keyed to the shaft 5 (-FIG. 3). A pilot bearing 38 isprovided between the end of the shaft 5 and the polar field member 21,thus forming an end support for the driven shaft 19 and the field member21.

FIG. 4 shows an end view of the spider 35 which will be seen to includea number of openings, flanked by pairs of long fins 41. Shorter fins 43are provided between the pairs of fins ii where no openings 39 exist.Outside of the openings 39 are located still shorter fins 45. Thespacings between each fin 41 and the adjacent fins 43 and 45 areunequal. All of the fins 41, 43 and 45 are curved to extend from aradial direction to an axial direction. In the latter direction theyabut aligned, axially disposed fins 47 on and extending from theinductor drum 33, as shown in FIG. 3.

When the motor 3 drives the drum 33 and the coil is excited, anelectromagnetic coupling effect is established into the known mannerbetween the drum and the polar field member 21. The speed of the drivenshaft 19 is a function of the excitation of the coil 25, the slip speedbetween the drum 33 and the polarizing teeth 23 resulting in theproduction of eddy currents in the inductor drum 33. These generate amagnetic field which reacts with the polar fields from the poles 23 totransmit torque between shafts 5 and 19.

The eddy currents generate a considerable amount of heat in drum 33,which must be carried away by the large current of air produced by thefins 41, 43, 45 and 47. The openings 39 and the variable angularspacings shown for the fins in FIG. 4 are designed for large air flowbut the variable spacing produces sound which has at least one or moredifferent characteristic frequencies or frequency peaks and which causesan undesirable highcnergy noise elfect. A typical condition of thisnature is illustrated in FIG. 10, in which line 1 plots the percentagesound level (in decibels) against frequency in cycles per second(c.p.s.). This line I shows peaks at PK and Q correspond to thefrequencies of 870 c.p.s. and 1300 c.p.s., respectively. Line II showsthe improvement effected by means of the invention. This shows not onlythat the sound level is generally reduced, but that the two particularlyobnoxious frequency peaks PK and Q, responsible for the more intolerablenoise-forming components of the sound, are practically eliminated. Thereason for this is the use in connection with the apparatus of the soundsuppressor assembly described below.

In order to accommodate and transmit the substantial Volume of air whichis circulated for cooling. 1 provide an extensive enclosure orrectangular plenum chamber P around the rotating parts. This may beformed by a reversible L-shaped housing part 49 connecting therectangular end walls 9 and 13. The L-shaped part 49 forms a top 51 andone side 53 of the chamber P. Thus the chamber P is formed on five sidesby the base 11, closed end walls 9 and 13, the flat top 51, and its flatside wall 53. The sixth side may thus be open before the soundsuppressor assembly or box, to be described and lettered S, is attached.When the assembly or box S is attached, this open side becomes coveredby the inner side of the box. Attachment is accomplished by any suitablemeans such as welding, bolting or the like. The suppressor box S carriesthe air inlet and outlet soundsuppressing means to be described.

Depending upon where the machine is tobe located, it may be desirable tohave air inlet and outlet means on one side or another of the machine,or it may even be desirable to have such means on top (see the dottedlines D, E and F of FIG. 9, showing alternative locations for box S).Which of these locatioins of suppressor S is to be employed depends uponthe desires of a customer, whether on the left, right-0r topside of theapparatus. To attach suppressor box S onthe'left side of plenum chamberP as shown in FIG. 1 (and at D in FIG. 9), the L-shaped part 49 will beset up on the right side. To position the suppressor box S on the rightside of the plenum chamber P, as shown at E on FIG. 9, involves merelyreversal of the position on end'walls 9 and 13 of the L-shaped member49. For top mountnig of box S, the top wall 51 may be omitted and twoside walls such as 53 employed, one on each of the left and right sidesof the machine.

Briefly, then, the rectangular plenum chamber P has five enclosingwalls, the sixth being provided by the attached rectangular suppressorbox S. Thus there is provided, on whatever is chosen as an open side ofthe plenum chamber P, an attached enclosing sound suppressor assembly S,through which inlet air is drawn and outlet air is expelled, in themanner explained below.

The sound suppressor box S has an inner wall 55, an outer or crosswall57, a top 59', a bottom 68, and side walls 61 and 63 (FIGS. 1, 2, 5 and6). It is divided interiorly by a vertical partition 66 and transverseshelves 6'7, 69 and 71, thereby forming three comparatively smallrectangular air inlet passages 73 and two rectangular larger air outletpassages 75. Vertical cross walls 77 divide each of the inlet passages73 into chambers MM and KK while vertical cross walls 79 divide each ofthe outlet passages into chambers M and K. Each of the air inletpassages 73 has a comparatively small aperture or opening 81 at itsouter end in wall 57, a comparatively large outlet opening 83 intoenclosure P at its inner end in wall 55, and an opening 85 ofintermediate size in its dividing cross wall 77 (FIG. 6). Each of theair outlet passages 75 likewise has a comparatively small aperture oropening 87 at an outer end, a comparatively large air inlet opening 89from enclosure P at its inner end, and an opening 91 of intermediatesize in its cross wall 79 (FIG. 5). The cross-sectional areas of theoutlet passages 75, including the openings 87, 91 and 89, are largerthan those of the inlet passages 73, including the openings 81, 85 and83, because the former carry expanded warmer air.

The box S, its dividing walls, and the openings 81, 83, 85, 37, 89 and91 are preferably all rectangular in form as the drawings show, becauseas such they are more economical to construct than are other shapes(e.g., circular or cylindrical) which may also be used in accordancewith this invention. Of importance in any event is that in a givenpassage the successive openings from the inside to the outside shalldecrease in area.

It will be noted from FIG. 2. of the drawings that the marginal portionsof each succeeding opening in either passages 73 or 75 lie within theaxially projected outline of the opening ahead of it. Thus, starting atthe side of the box S on its side adjacent plenum chamber P, for eachpassage there is a comparatively large opening (outside dotted line).Then moving axially along the passages in a direction away from theenclosure, the next intermediate opening (intermediate dotted line) lieswithin the projected outline of the first opening, and the outsidecomparatively small opening (solid lines) lies within the projectedoutline of the intermediate opening.

Thus as to inlet passages 73 (FIG. 6), each of intermediate openings 85should preferably be about 540% less in area than each of openings 83,and each of openings 81 should preferably be about 5-30% less in areathan each of the openings 85; likewise, in the case of outlet passages75 (FIG. 5), each of the areas of openings 91 should preferably be aboutS30'% less than that of each of the openings 89, and the area of each ofthe outer openings 87 should be about 530% less than that of each of theintermediate openings 91. These figures are subject to some variationwithin the principles of the invention. The purpose of the variation inopening sizes is that the portions around openings 91 and 87 on the onehand, and 85 and 81 on the other hand, shall function to reflectoutgoing sound backwardly, so as to have a substantial, if not complete,resonant sound-cancelling effect, to be discussed. In the case ofinletpassages 73 (FIG. 6), sound-reflecting wooden or like filler blocks93, 95 and 97 are employed on the insides of the inlets for purposeswhich will appear. In FIG. 6A is shown how acoustical lining material92, such as glass wool, may be used in any or all inlet and outletpassages. Such material tends to absorb sound of higher frequencies,e.g., above about 2000 c.p.s. However, sound absorbent linings are adesirable but not necessary feature for operation according to theinvention.

Air is drawn into and through the inlet passages 73, being impelledthrough the plenum chamber P by the sound-producing, finned rotatingspider 35- and inductor drum 33. The air then is driven out through theoutlet passages 75.'The sound to be suppressed passes out from theplenum chamber P through both passages 73 and 75. Thus the sound ispropagated oppositely to the inlet flow of air in inlet passages 73(FIG. 6) and in the same direction as that of the flow of exhaust airthrough the outlet passages 75 (FIG. 5).

FIGS. 5 and 6 as above described show preferred forms of the passages 73and '75, which require only a comparatively shallow form of box S, asshown in FIG. 1. In FIGS. 7 and 8, corresponding but longer passages areemployed, requiring a deeper but still useful form of box S. Numeralsused in FIGS. 7 and 8 correspond to those employed for like functioningparts in FIGS. 5 and 6, except that they are primed in FIGS. 7 and 8because of certain dimensional differences. Operation will be describedfirst by reference to theforms of FIGS. 7 and 8, because explanation asto these forms the basis for making clear certain advantages of the formof sound suppressor assembly S shown in FIGS. 5 and 6.

As to operation (FIGS. 7 and 8), the speed of sound in still air at roomtemperature is taken herein as being approximately 1129 f.p.s. The speedof air in through the inlet passages 73' and out through the outletpassages 75 is taken to be approximately 150* f.p.s. The algebraic sumof these speeds in each passage 75 is approximately 1279 f.p.s. and ineach passage 73 is approximately 979 f.p.s. The velocity (v), frequency(f) and wavelength (w) of sound in air are related by the expressionv/f=w. The characteristic frequency or sound frequency peak generated byrotary induction apparatus is a function of the rotational speed of thefinned or vaned drum 33' and the number of peripheral fins and openings39. As there are at least two different peripheral spacings between thevarious fins and two different sized openings 39', as noted above, thesound generated by operation of this apparatus has at least twodifferent characteristic frequencies or frequency peaks as shown ingraph I of FIG. 10.

Consider first the higher frequency peak of 1300 c.p.s. at Q in FIG. 10.Substituting values in the above-stated expression and converting toinches, there results 12= 11.8 inches (wavelength) The inside dimensionbetween the openings 91 and 87 (i.e., the portions of outlet passages 75within resonant chambers H) is made to correspond substantially to thiswavelength (FIG. 7). Next consider the lower frequency of 870 tips. atPK in FIG. 10. Substituting values in the above expression andconverting to inches, there will result The inside dimension betweenopenings 89' and 91 (i.e., the portions of the outlet passages 75'within resonant chambers J) is made to correspond substantially to thiswavelength (FIG. 7 Thus in effect the outlet passages 7 5 are divide-clinto chambers H and J, the effective inside lengths of which areapproximately 11.8 inches and 17.65 inches, respectively, which is tosay, about equal to the wavelengths at the peaks Q and PK in FIG. 10under the air velocity conditions existing in these chambers. Eachchamber H is substantially resonant at the higher characteristicfrequency and a standing wave at this character- X 12-- 17.65 inches(Wavelength) istic frequency is produced by sound reflection from aroundits opening 87'. As the reflected wave is effectively substantially outof phase with sound of this frequency peak leaving the enclosure, thereis substantial cancellation of sound at or near the 1300 c.p.s. peak Q.In the same fashion, each chamber J resonates at or near the 870 c.p.s.peak PK. In the latter case, sound of this lower frequency reflects fromaround opening 91 and forms a standing wave in chamber I. As thereflected wave is effectively substantially 180 out of phase with thesound waves of this characteristic frequency generated by coupling 1,there is substantial cancellationof sound of this frequency.

As regards the passages 73 (FIG. 8), the outgoing sound progressesagainst the inlet how of air so that the chamber lengths (in this casethe chambers are letters H and I) need to be computed with an airvelocity of 1129150 =979 f.p.s. By computations similar to those abovegiven and taking the negative sign into account, there will be obtainedan inside length for chamber H of 9.05 inches and for chamber 1 of 13.6inches. In order that such lengths may be conveniently obtained in thebox S, wooden spacers such as shown at 93 and 95' are employed, as shownin FIG. 8. Thus the inside lengths 9.05 inches :of chamber H and 13.6inches of chamber J effect substantial resonance at the peaks PK and Q(FIG. 10) under the conditions existing in these air inlet passages. Thenet sound-suppressing effect of box S is as shown in FIG. 10; whereinthe primary noiseproducing peaks are suppressed as shown by curve IIrelative to curve I. There will also be reflections from the marginsaround openings 81 and 87 through the entire approximately 30-inchlength of each inlet 73 and each outlet 75. However, as this length doesnot substantially correspond to :a wavelength function of a soundfrequency peak generated by this particular coupling, it would have nosignificant silencing effect. If a third characteristic frequency isproduced by the rotary apparatus, sound of this frequency can be sharplyattenuated by use of another chamber of the proper length, or it will beattenuated if the combined lengths of H and J are approximately awavelength function of this thirdsound frequency.

The term wavelength function as used herein refers to one or one-halfwavelength, or multiples thereof (under conditions existing in theparticular passage of the sound suppressor assembly), of sound of acharacteristic frequency to be suppressed. That is, the velocity and temperature of the air significantly affect the propagation velocity of thesound Wave relative to the enclosure, and this will change thewavelength. As noted above, one wavelength of sound having acharacteristic frequency of 1300 cycles is about 11.8 inches in outletpassage 75', while one wavelength of sound of this same characteristicfrequency is about 9:05 inches in inlet passage 73 because thepropagation velocity of the sound relative to the apparatus enclosure isassumed by this example to be 300 f.p.s. greater in the air outletpassage than in the air inlet passage. Thus, although these distances ofH and H are quite different, each corersponds to the same wevelen-gthfunction of the same characteristic frequency of sound in the aircirculating through the respective passages.

While as above stated the resonant chambers H, J (FIG. 7) and H, 1 (FIG.8) accomplish the desired results, I have found that the added orextended 30-inch or so lengths of these can be reduced, and consequentlythe depth of the sound box S reduced, as shown by box S in FIGS. 1, 5and 6.

In FIG. 5 the lengthwise chamber dimensions are what may be referred toas coextensive. Thus, the 17.65-inch dimension (which corresponds asnoted above to one wavelength of 870 c.p.s. sound in the conditionsassumed here to exist, for example, in the air outlet passages)constitutes the full depth of the shallower box S and corresponds to thelength of a resonant chamber L which has a length equal to the combinedlengths of chambers M and K. Chambers K have a length of l1.8 inches (:1full wavelength of sound of a frequency of 1300 c.p.s. in the conditionsassumed to exist in this example in the air outlet passages) andresonate at this 1300 c.p.s. frequency peak. The sound-suppressingresults are similar but the suppressor box S (FIGS. 1, 5 and 6) is muchshallower than suppressor box S (FIGS. 7 and 8). If desired, chamber Mmay be utilized instead or", or in addition to, chamber K if the lengthR of this chamber is made a wavelength function of a sound frequencypeak to be suppressed.

Referring now to the preferred shorter forms of the air inlet passages73 shown in PEG. 6, the length LL from the inner surface of block 93 tothe outer surface of block 97 is 13.6 inches and thus corresponds to onewavelength of the sound characteristic frequency of 870 c.p.s. in aircirculating in that passage. Similarly, the length of chamber KK is 9.05inches, which is one wavelength of the 1300 c.p.s. frequency peak in theair circulating in this inlet passage. Thus, the lengths of the resonantchambers LL and KK correspond to the wavelength functions of 13.6 inchesand 9.05 inches shown in FIG. 8 except that these dimensions are in acoextensive or folded relationship in FIG. 6, thereby permitting the useof a smaller depth for the sound box S. It will be noted that in theshallow form of the box S illustrated in FIGS. 5 and 6, the overalloutside depth for both inlet passages 73 and the outlet passages 75 isthe same, but by reason of the use of wood blocks 93, 95 and 97 in theinlets 73 the desired shorter physical lengths of these resonantchambers KK and LL are effected conveniently.

It is to be understood that while the lengths of the various resonantchambers have been made substantially equal to one full wavelength ofsound of typical assumed characteristic frequencies under the conditionsassumed to exist in these particular passages, alternately these lengthsmay be made substantially equal to half-wavelengths of sound of thecharacteristic frequencies, and the overall depths of these soundsuppressor assemblies may thus be halved.

Referring now to FIGS. 11-14, another sound suppressor assembly of thepresent invention is illustrated. This assembly, indicated generally atS", is particularly useful when the sound produced by the rotaryapparatus has one predominant frequency peak or characteristic frequency(for example, where a constant spacing distance is maintained betweenthe vanes of fins of the air moving member). Two air inlet openings forthe enclosure P are indicated at 99 and a single air outlet for thisenclosure is indicated at 101. Two parallel air inlet passages 103 flowthrough apertures 117 and passages 103. Wall is spaced away fromopenings 99 a distance approximately corresponding to a wavelength (orone-half wavelength or multiple thereof) of the single predominant soundcharacteristic frequency to be suppressed. An air outlet passage llfifor enclosure P is provided through a chamber U formed between airoutlet 101i and cross wall 115 having an opening or aperture 121. As thewidth of suppressor assembly is greater than the length of the enclosureP, two closure panels 3.23 and are welded to the adjacent assembly andenclosure portions to close the rectangular gaps which would otherwiseremain.

In this embodiment, the lengths of the inlet and outlet passages areshown to be equal, and this will effect substantial noise suppression atthe single characteristic frequency if this length is made substantiallyequal to a wavelength function of this characteristic frequency (i.c.,without correcting for the effects of temperature etc. in the chambers Tand U). As the Q of the apparatus may not be particularly high, thisapproximation may be satisfactory. For even more effective noisesuppression, the length of the air outlet and inlet passages may be mademore precisely equal to one-half or one wavelength (or a multiplethereof) of the characteristic sound frequency considering the airvelocity and temperature within the chambers T and U. Thus, the chamberU should be made sufiiciently longer to equal the wavelength of thissound frequency peak in the eiliuent hotter air passing through outletpassage 119 while the chambers T are made shorter to equal thewavelength of this sound frequency peak being propagated against thedirection of cooler entering air flowing through inlet passages 103. Foreven more precise calculations the temperatures in the inlet and outletpassages under typical or average operating conditions should be takeninto account. Also, it will be noted that the diagonal dimensions of theresonant chambers should not be made approximately equal to thewavelength function of a sound frequency peak to be suppressed, as thiswould tend to reduce the efficiency of sound suppression.

It will be understood that the cross wall apertures or external openingsmay be connected to any desired air supply and exhaust ducts, and thatthese sound suppression units of this invention offer very littlerestriction to the passage of air or gas coolant into and out of themachine. Moreover, it has been found that sound suppressed machines ofthis invention may have a sound level as low as only about 1% of thesound level produced without the sound suppression system of thisinvention.

In view of the above, it will be seen that the several objects of theinvention are accomplished, namely, the provision of an air-cooleddynamoelectric machine which for one thing has a high-handling capacitydue to large air flow which is accommodated by the extended form of thesurrounding plenum chamber. The plenum chamber P is preferably polygonalfor accommodating in any one of several positions the rectangularsuppressor box containing air outlet and inlet means. Moreover, th meansfor dividing the inlets and outlets into substantially resonant chambersor segments suppresses noise-forming sound level peaks such as PK and Q(FIG. 10). Also, this is done in such a way that the entire soundsuppressor box S may be made in rectangular form and of simple flatsheets.

As various changes could be made in the above constructions withoutdeparting from the scope of the in vention, it is intended that allmatter contained in the above description or shown in the accompanyingdrawings shall be interpreted as illustrative and not in a limitingsense.

What is claimed is:

l. A dynamoelectric machine comprising electromagnetic inductionapparatus having two relatively rotary members which generate heatduring relative 9. rotation, one of said members including means formoving air at a velocity which is a function of the rotational speed ofsaid one member, said one member producing sound which has at least onecharacteristic frequency which is a function of the speed of said onemember, and enclosure for said apparatus having at least one air inletopening and at least one air outlet opening, means extending from eachof said air inlet and outlet openings and forming an air inlet passageand an air outlet passage, each passage connected at one end with theenclosure and having a cross wall positioned transversely to thedirection of air flow therethrough, the cross walls having aperturessmaller than said respective inlet and outlet openings and axiallyspaced therefrom in a direction away from said enclosure and atdistances substantially equal to a wavelength function of saidcharacteristic frequency of said apparatus thereby to effect substantialcancellation of sound at said frequency and substantially reduce thenoise level of said machine.

2. A dynamoelectric induction apparatus as set forth in claim 1 whereinthe distance between the air inlet opening and its respective cross wall.is less than the distance between said air outlet opening and itsrespective cross wall, each of said different distances beingsubstantially the same wavelength function of said characteristicfrequency of the sound in the air circulating through the respectivepassages.

3. A dynamoelectric machine comprising electromagnetic inductionapparatus having two relatively rotary members which generate heatduring relative rotation, one of said members including means for movingan at a velocity which is a function of the rotational speed of said onemember, said one member producing sound which has at least twocharacteristic frequencies which are functions of the speed of said onemember, an enclosure for said apparatus having at least one air inletopening and at least one air outlet opening, means extending from saidair inlet and air outlet openings respectively and forming an air inletpassage and an air outlet passage each connected atone end with theenclosure, each of the inlet and outlet passages having a first and asecond cross wall positioned transversely to the direction of airflowtherethrough and axially spaced different distances from the respectiveinlet and outlet openings in a direction away from said enclosure, thevcross wall being smaller than that of the aperture in the respectivefirst cross wall, the spacing between one of said cross walls and therespective opening being substantially equal to a wavelength function ofone of said characteristic sound frequencies thereby to effectsubstantial cancellation of sound of one of said characteristicfrequencies and greatly reduce the noise level of said machine.

4. A dynamoelectric machine as set forth in claim 3 in which the spacingbetween the other cross wall and the respective opening of each of thepassages is substantially equal to a wavelength function of the other ofsaid characteristic sound frequencies thereby to effect substantialcancellation of sound of both of said frequencies.

5. A dynamoelectric induction apparatus as set forth in claim 4 whereinthe distances between the air inlet opening and the respective crosswalls are each less than the respective distances between said airoutlet opening and the respective cross walls, each of said differentdistances being substantially thesame wavelength functions of saidcharacteristic frequencies of the sound in ,the air circulating throughthe respective passages.

said passages is substantially equal to a wavelength function of theother of said characteristic sound frequencies thereby to effectsubstantial cancellation of sound of both of said frequencies.

7. A dynamoelectric induction apparatus as set forth in claim 6 whereinthe distances between the air inlet opening and the respective crosswalls are each less than the respective distances between said airoutlet opening and the respective cross walls, each of said differentdistances being substantially the same wavelength functions of saidcharacteristic frequencies of the sound in the air circulating throughthe respective passages.

8. A dynamoelectric machine as set forth in claim 3 in which the spacingbetween each of the second cross walls and the respective opening issubstantially equal to a wavelength function of the lower of said twocharacteristic frequencies, and the spacing between each of the firstcross walls and the respective opening is substantially equal to awavelength function of the higher of said two characteristic frequenciesthereby to effect substantial cancellation of sound of both of said hequencies.

9. A sound suppressor assembly for an electromagnetic inductionapparatus having two relatively rotary members which generate heatduring relative rotation, one of said members including means for movingair at a velocity which is a function of the rotational speed of saidone member, said one member producing sound which has at least onecharacteristic frequency which is a function of the speed of said onemember, said apparatus including an enclosure having at least one airinlet opening and one air outlet opening; said sound suppressor assemblycomprising means extending from each of said air inlet and air outletopenings thereby forming an air inlet passage and an air outlet passage,each passage being adapted for connection at one end with the enclosureand having a cross wall positioned transversely to the direction of airfiow therethrough, the cross walls having apertures smaller than saidrespective inlet and outlet openings and axially spaced therefrom in adirection away from said enclosure and at distances substantially equalto a wavelength function of said characteristic frequency of saidapparatus thereby to effect substantial cancellation of sound atsaidfrequency and substantially reduce the noise level of said apparatus.

10. A sound suppressor assembly as set forth in claim 9 wherein thedistance between the air inlet opening and its respective cross wall isless than the distance between said air outlet opening and itsrespective cross wall, each of the different distances beingsubstantially the same wavelength function of said characteristicfrequency of the sound in the air circulating through the respectivepassages.

11. A dynamoelectric machine comprising rotary electromagnetic inductionapparatus including a sound-generating gas-coolant circulating device, aplenum chamber surrounding said apparatus, means extending from theplenum chamber forming a passage connected at one end with the plenumchamber by a first comparatively larger opening, and having a wallcontaining a comparatively smaller second openin axially spaced from thefirst opening, both of'said openings having surrounding marginalportions transverse to said passage, the marginal portion of said secondopening extending within the axially projected outline of the firstopening, the openings of said passage carrying air moved by saidcirculating device and carrying sound waves moving from the larger firstopening to the smaller second opening for reflection by said marginalportion of the second opening back toward the plenum chamber. a

12. A dynamoelectric machine comprising rotary electromagnetic inductionapparatus including a sound-generating gas-coolant circulating device, aplenum chamber surrounding said apparatus, means extending from theplenum chamber forming a passage connected at one end with the plenumchamber by a first comparatively larger opening, said means having anouter end wall containing a comparatively smaller second opening axiallyspaced from the first opening and having an intermediate cross wallcontaining a third opening of intermediate size, all of said openingshaving surrounding marginal portions transverse to said passage, themarginal portion of said second opening extending within the axiallyprojected outline of the intermediate opening, the marginal portion ofthe intermediate opening extending within the projected outline of thefirst opening, the opening of said passage carrying air moved by saidcirculating device and carrying sound waves moving from the larger firstopening to the intermediate and second openings for reflection by saidmarginal portions of the intermediate and second openings back towardthe plenum chamber.

13. A dynamoelectric machine comprising rotary electromagnetic inductionapparatus including a sound-generating gas-coolant circulating device, aplenum chamber surrounding said apparatus, means extending from theplenum chamber forming passages, each passage connected at one end withthe plenum chamber by a first comparatively larger opening, and having awall containing a comparatively smaller second opening axially spacedfrom the first opening, both openings in each passage having surroundingmarginal portions transverse to the passage, the marginal portion ofsaid second opening extending within the axially projected outline ofthe first opening, the openings of one of said passages carrying air tothe plenum chamber, the openings of the other passage carrying air fromthe plenum chamber, each of said passages carrying sound waves movingfrom its larger first opening to its smaller second opening forreflection by said marginal portion of the second opening back towardthe plenum chamber.

14. A dynamoelectric machine comprising rotary electromagnetic inductionapparatus including a sound-generating gas-coolant circulating device, aplenum chamber surrounding said apparatus, means extending from theplenum chamber forming passages, each passage connected at one end withthe plenum chamber by a first comparatively larger opening and having awall containing a comparatively smaller second opening axially spacedfrom the first opening and having an intermediate cross wall containinga third opening of intermediate size, all of said openings havingsurrounding marginal portions transverse to said passage, the marginalportion of said second opening extending within the axially projectedoutline of the intermediate opening, the marginal portion of theintermediate opening extending within the projected outline of the firstopening, the openings of one of said passages carrying air to the plenumchamber, the openings of the other passage carrying air from the plenumchamber, each of said passages carrying sound waves moving from itslarger first opening to its intermediate and' second openings forreflection by said marginal portions of the second and intermediateopenings back toward the plenum chamber.

15. A dynamoelectric machine comprising rotary electromagnetic inductionapparatus including sound-generating gas-coolant circulating means, aplenum chamber surrounding said means, a sound suppressor assembly, saidassembly having an outer wall and an inner wall, the latter comprising aportion of the wall of the plenum chamber, said assembly being formedwith at least one air inlet passage and at least one air outlet passage,each passage extending from said outer wall to said inner Wall, eachpassage also including an intermediate cross wall dividing it intosections, the inner wall, intermediate cross wall and outer wall in eachpassage having axially related openings of respectively progressivelysmaller areas through which air is moved into and forced out of theplenum chamber through said inlet and outlet passages respectively whilesound moves out from the plenum chamber through both passages forreflection from the margins of the outer and intermediate openingstoward the plenum chamber.

16. A dynamoelectric machine made according to claim 15, wherein saidsections into which said passages are divided by their cross walls areof unequal lengths.

17. A dynamoelectric machine comprising rotary electromagnetic apparatusincluding a sound-generating gascoolant circulating device, a polygonalplenum chamber surrounding said apparatus constructed to provide anopening on one side or another thereof for attachment thereat of a soundsuppressor assembly, a sound suppressor assembly in the form of a boxhaving an outer wall and an inner wall, the latter forming a closure forsaid opening of the plenum chamber, said assembly having several airinlet passages and several air outlet passages, each passage extendingfrom said outer wall to said inner wall, each passage also including anintermediate Wall dividing it into unequal sections, said inner wall,intermediate wall and outer wall having aligned openings withprogressively smaller areas in that order through which air is drawninto and forced out of the plenum chamber through said inlet and outletpassages respectively, the inner margins of the openings in theintermediate wall and the outer wall forming sound-reflecting means forsubstantially reducing noise by sound waves moving outwardly through thepassages.

18. A dynamoelectric machine made according to claim 17, wherein saidplenum chamber, said assembly, said passages and the openings are all ofrectangular form.

19. A dynamoelectric machine comprising rotary electromagnetic apparatusincluding a gas-coolant circulating device producing sounds includingthose substantially at one frequency peak, a plenum chamber surroundingsaid apparatus, coolant-passage-forming means extending from the plenumchamber, said passage-forming means terminating at one end in a wallforming part of the plenum chamber, said chamber having a second wall,openings in the walls, the opening in the wall forming part of theplenum chamber being larger than the other opening, the length of thepassage-forming means between said walls being approximately equal to awavelength function of said frequency peak of the sound generated bysaid induction apparatus.

2i). A dynamoelectric machine comprising rotary electromagneticapparatus including a gas-coolant circulating device producing soundsincluding those substantially at two frequency peaks, a plenum chambersurrounding said apparatus, coolant-passage-forming means extending fromthe plgpum chamber, said passage-forming means terminating at one end ina first inner wall forming part of the plenum chamber, said chamberterminating at its other end in a third outer wall and having a secondintermediate wall, openings in the first, second and third Walls whichare progressively smaller in that order, the intermediate walldetermining lengths in the passage-forming means between two pairs ofthe walls approximately equal to wavelength functions of said twofrequency peaks of sound generated by said induction apparatus.

21. A dynamoelectric machine comprising rotary electromagnetic apparatusincluding a gas-coolant circulating device producing sounds includingthose substantially at two frequency peaks, a plenum chamber surroundingsaid apparatus, coolant-passage-forming means extending from the plenumchamber, said passage-forming means terminating at one end in an innerend wall forming part of the plenum chamber, said chamber terminating atits other end in an outer end wall and having an intermediate wall,openings in the inner end wall, intermediate wall and the outer end wallwhich are progressively smaller in that order, the distance between theintermediate wall and one of the end walls being approximately equal toa wavelength function of one of said frequency peaks of sound generatedby said apparatus, and the distance between the inner and outer endwalls being approximately 13 equal to a wavelength function of the otherof said frequency peaks of sound generated by said apparatus.

,22. A dynamoelectric machine comprising rotary electromagneticapparatus including a gas-coolant circulating device producing soundsincluding those substantially at two frequency peaks, a plenum chambersurrounding said apparatus, coolant passage-forming means extending fromthe plenum chamber, said passage-forming means terminating at one end ina first inner wall forming part of the plenum chamber, said chamberterminating at its otherend in a third outer wall and having a secondintermediate wall, openings in the first, second and third walls whichare progressively smaller in that order, the distance between theintermediate wall and the first wall being approximately equal to awavelength function of the higher frequency one of said peaks of soundgenerated by said induction apparatus, and the distance between theinner and outer end walls being approximately equal to a wavelengthfunction of the lower frequency one of said peaks of sound generated bysaid apparatus.

23. A dynamoelectric machine comprising rotary electromagnetic apparatusincluding a gas-coolant circulating device producing sounds includingthose substantially at two frequency peaks, a plenum chamber surroundingsaid apparatus, coolant-passage-forming means extending from the plenumchamber, said passage-forming means terminating at one end in a firstinner wall forming part of the plenum chamber, said chamber terminatingat its other end in a third outer wall and having a second intermediatewall, openings in the first, second and third walls which areprogressively smaller in that order, the distance between theintermediate wall and one end wall being approximately equal to awavelength function of one of said frequency peaks of sound generated by,said induction apparatus, and the distance between said intermediatewall and the other end wall being approximately equal to .a wavelengthfunction of the other of said frequency peaks of sound generated by saidapparatus.

2 4. A dynamoelectric machine comprising rotary electromagneticapparatus including a sound-generating gascoolant circulating deviceproducing sound, a plenum chamber surrounding said apparatus, a soundsuppressor assembly attached to said plenum chamber, said assemblycomprising a substantially rectangularly formed box interiorly dividedby substantially rectangularly formed walls and shelves dividing the boxinto at least one gas inlet passage and at least one gas outlet passage,each passage having an interior opening communicating through an insidewall with the plenum chamber through an intermediate wall in the passageand through an outside wall of the box, the sizes of the openings in theinside, intermediate and outside walls decreasing in area in that order.

25. Dynamoelectric apparatus according to claim 24, wherein saidopenings are of rectangular form.

26. A dynamoelectric machine comprising rotary electromagnetic apparatusincluding a sound-generating gascoolant circulating device producingsound, a plenum chamber surrounding said apparatus, a sound suppressorassembly attached to said plenum chamber, said assembly comprising asubstantially rectangular formed box interiorly divided by substantiallyrectangularly formed walls and shelves to form several rectangular gasinlet passages and several rectangular gas outlet passages, each passagehaving an interior opening communicating with the plenum chamber, anopening in an intermediate wall, and an opening in an outlet wall of thebox, the sizes of the openings in the interior, intermediate and outletopenings decreasing in area.

27..Dynamoelectric apparatus according to claim 26, wherein each of saidopenings is rectangular.

28. A dynamoelectric machine comprising rotary electromagnetic apparatusincluding a sound-generating gascoolan-t circulating device producingsound, a substantially rectangular plenum chamber surrounding saidapparatus, a sound suppressor assembly in the form of a box attached onone of its sides to a side of said plenum chamber, said assembly beinginteriorly divided by substantially rectangularly formed walls andshelves dividing the box into several rectangular gas inlet passages andseveral rectangular gas outlet passages, each passage being segmented bya cross wall, each passage having an inner rectangular openingcommunicating with the plenum chamber, an intermidate rectangularopening in its cross wall and a rectangular outer openingin an outletwall of the box, the areas of the inner, intermediate and outsideopenings decreasing in that order.

